The user file-creation mode mask (umask) is used to determine the file permission for newly created files. It can be used to control the default file permission for new files. It is a four-digit octal number.

Setting the UMASK

You can setup the umask value in /etc/bashrc or /etc/profile for all users. By default, most Linux distros set it to 0022 (022) or 0002 (002).

Open /etc/profile (global) or ~/.bashrc file

# vi /etc/profile

or

$ vi ~/.bashrc

Append/modify the following line to setup a new umask:

umask 022

Save and close the file. Changes will take effect after next login.

But what is 0022 and 0002?

The default umask 0002 is used for regular users. With this mask, default directory permissions are 775, and default file permissions are 664.

The default umask for the root user is 0022, and as a result, default directory permissions are 755, and default file permissions are 644.

For directories, the base permissions are 0777 (rwxrwxrwx) and for files they are 0666 (rw-rw-rw).

To calculate directory permissions for a umask value of 022 (root user):

The following example explains the steps needed to set a umask value that will result in permission values 700 for directories and 600 for user files. The idea very simply is that only the user will be allowed to read or write the file, or to access the contents of the directory.